Add eslint-plugin-compat.

We can check for browser compatibility on lint time now.

package-lock.json

@@ -1071,6 +1071,12 @@
         "map-obj": "1.0.1"
       }
     },
+    "caniuse-db": {
+      "version": "1.0.30000671",
+      "resolved": "https://registry.npmjs.org/caniuse-db/-/caniuse-db-1.0.30000671.tgz",
+      "integrity": "sha1-nwcbvHuWmUY4zLr0eCnVihV3qO0=",
+      "dev": true
+    },
     "caniuse-lite": {
       "version": "1.0.30000732",
       "resolved": "https://registry.npmjs.org/caniuse-lite/-/caniuse-lite-1.0.30000732.tgz",
@@ -1771,6 +1777,30 @@
         }
       }
     },
+    "eslint-plugin-compat": {
+      "version": "1.0.4",
+      "resolved": "https://registry.npmjs.org/eslint-plugin-compat/-/eslint-plugin-compat-1.0.4.tgz",
+      "integrity": "sha512-16yjDdjrivRQT7/Kov+3O6DMvfg8WYC1JKPAsvf/UNtdLBeMXVYATohAM4nOak1ynGP69mKUlOjw7nroUqY9Sg==",
+      "dev": true,
+      "requires": {
+        "babel-runtime": "6.26.0",
+        "browserslist": "2.1.4",
+        "caniuse-db": "1.0.30000671",
+        "requireindex": "1.1.0"
+      },
+      "dependencies": {
+        "browserslist": {
+          "version": "2.1.4",
+          "resolved": "https://registry.npmjs.org/browserslist/-/browserslist-2.1.4.tgz",
+          "integrity": "sha1-zFJq9KExK30uBWU+VtDIq3DA4FM=",
+          "dev": true,
+          "requires": {
+            "caniuse-lite": "1.0.30000730",
+            "electron-to-chromium": "1.3.21"
+          }
+        }
+      }
+    },
     "eslint-scope": {
       "version": "3.7.1",
       "resolved": "https://registry.npmjs.org/eslint-scope/-/eslint-scope-3.7.1.tgz",
@@ -5501,6 +5531,12 @@
         "resolve-from": "1.0.1"
       }
     },
+    "requireindex": {
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/requireindex/-/requireindex-1.1.0.tgz",
+      "integrity": "sha1-5UBLgVV+91225JxacgBIk/4D4WI=",
+      "dev": true
+    },
     "resolve": {
       "version": "1.4.0",
       "resolved": "https://registry.npmjs.org/resolve/-/resolve-1.4.0.tgz",